Styrene-acrylate-itaconic acid latex



United States Patent 3,301,806 STYRENE-ACRYLATE-ITACONIC ACID LATEX Leonard F. Guzialk, Pittsburgh, and William N. Maclay, Monroeville, Pa., assignors to Koppers Company, Inc.,

a corporation of Delaware No Drawing. Filed July 17, 1962, Ser. No. 210,592 2 Claims. (Cl. 26029.6)

This invention relates to synthetic latices and in particular to a new styrene-acrylate latex having improved properties.

In the co-pending application of L. F. Guziak, Serial No. 191,872, filed May 2, 1962, now US. Patent No. 3,232,899, there are disclosed reconstitutable latices useful in the preparation of surface coating compositions comprised by weight of from 20-60 parts of a vinyl aryl monomer, from -40 parts of an unsaturated ester, and from 10-40 parts of an unsaturated acid. The water redispersible feature requires a minimum of 10' parts of unsaturated acid.

Quite surprisingly, we have found that a multipolymer composed of a vinyl aryl monomer, an unsaturated ester, and a reduced quantity of a specific unsaturated acid, provides a latex having considerably improved properties over known vinyl aryl mono=mer-unsaturated ester latices. The new latex, when used as a component in conventional water base baked primers for metallic surfaces, has shown improved intercoat adhesion between the prime coat and an acrylic finished top coat. Further, when used as a component in conventional water based paints, the new latex imparted high scrub resistance to the coating.

It is, therefore, an object of our invention to prepare a new styrene-acrylate latex having improved properties.

In accordance with the invention,-we have discovered a new latex composition comprising an aqueous dispersion of a vinyl aryl monomer, an acrylic ester and from 0.5-1.5 percent by weight of itaconic acid. These monomers are copolymerized to produce a grain-free, coagulum-free latex normally having a particle size of from 0.1 to 0.3 micron.

The vinyl aryl monomer of this novel composition may be styrene, o-methylstyrene, rn-methylstyrene, p-methylstyrene, ethylstyrene, dimethylstyrene, alpha-methylstyrene, p-chlorostyrene, p-methoxystyrene, and the like; 2, 4-dichlorostyrene, 2,5-diohlorostyrene, p-bromostyrene, alpha-methyhp-methylstyrene, p-isopropylstyrene, vinyl napthalene, etc. Mixtures of two or more such compounds may be used if desired.

The unsaturated copolymerizable acrylic esters to be used in accordance with the present invention are straight chain or branch chain aliphatic alcohol esters of acrylic or methacrylic acid. The alcohol radicals should be saturated and should contain from 1-20 carbon atoms. When the number of carbon atoms in the alcohol radical exceeds twenty, the resultant latices will dry to form films which will be too soft and too tacky for surface coating applications. Within the limitations set above, a wide variety of acrylic and met-hacrylic acids may be used. Typical are the esters formed by esterifying acrylic or methacrylic acid with an alcohol, such as ethyl alcohol, butyl alcohol, amyl alcohol, hexa-nol, Z-ethyl hexanol, 2- methyl pentanol, the oxo-alcohol of an isobutylene dimer, heptyl alcohol, 3-methylheptyl alcohol, the oxo-alcohol of an isobutylene trimer, the oxo-alcohol of a propylene dimer, the oxo-alcohol of a propylene tetramer, cetyl alcohol, dodecyl alcohol, tridecyl alcohol, tetradecyl alco hol, etc. Mixtures of such arcylic or methacrylic acid esters may be used if desired.-

At the present time, itaconic acid is the only unsaturated iacid useftfl in this invention. Irtaconic acid is a dibasic acid having an activated double bond of the formula:

O 0 OH CH2=O CHaGOOH Its higher carboxyl content over other unsaturated acids and its unique beta-carboxyl group are responsible for producing the improved latex of this invention.

The latex 0f the present invention is produced by interpolymerizing the foregoing components within a specific range of proportions. The vinyl aryl monomer content should comprise by weight of from 50-70 percent of the total monomers, in which the range between 54-58 percent is preferred. The unsaturated ester components should comprise from 29-49 percent by weight of the toad monomer, in which the preferred range is from 41.5 to 45.5. If the percent of unsaturated ester is increased, the film produced is tacky at the lowest film-forming temperatures. On the other hand, if the unsaturated ester component is decreased below the minimum given above, the film does not coalesce except by the addition of external coalescing agents or plasticizers. The itaconic acid content should comprise by weight from 0.5 to 1.5 percent of the total monomer, the preferred range being about 0.5-0.75 percent. Using less than the minimum amount of itaconic acid results in the formation of a latex having unsatisfactory mechanical stability, which is determined by the formation of coagulum during mixing or other mechanical agitation. On the other hand, using more than the maximum amount of itaconic acid results in decreased conversion of the latex to below the acceptable range of 96-100 percent.

Preparation of the novel grain-free, coagulum-free latex is carried out by an aqueous emulsion polymerization reaction. Preferably, the ingredients of the polymerization formulation are premixed to form six essential charges: Reactor charge, catalyst charge A, catalyst charge B, monomer charge I, monomer charge II, and monomer charge III.

The reactor charge comprises essentially the major por-- tion of water used in the reaction, which should be substantially oxygen-free. The total amount of water used can be varied according to the solids content desired in the final latex. It is generally preferred to use a ratio of water to monomer such that a latex, having a solids content, i.e. copolymer, surfactants and electrolytes, of from 40-65 percent, is produced. The preferred range of solids is from 48-55 percent.

The catalyst charge A comprises a major portion of the polymerization catalyst, the emulsifiers and conventional polymerization aids, such as buffers, particle size regulators, activators, etc., dissolved in a minor amount of the water requirement. Useful catalysts for the preparation of the latex are the conventional polymerization catalysts, such as sodium persulfate, potassium persulfate, ammonium persulfate, benzoyl peroxide, lauroyl peroxide, di-tbutyl peroxide, cumene hydroperoxide, azobisisobutyronitrile, etc. Mixtures of two or more such polymerization catalysts may be used if desired. The amount of catalysts to be used is conventional and generally falls within the range of 0.01 to 1 part of polymerization catalyst per 100 parts of monomer mixture. In preparing the catalyst charge, any of the conventional emulsifying agents may be used alone or in admixtures. These include, alklai metal salts of long chain alkyl sulfates and sulfonates, ethylene oxides of long chain fatty acids, alcohols or mercaptans, sodium salts of sulfonated hydrocarbons, alkaryl sulfonates, etc. Representative emulsifiers include compounds such as sodium lauryl sulfate, sulfosuccinic acid esters, the Z-ethylhexyl esters of sulfosuccinic acid,

sodium salts of dioctyl sulfosuccinic acid, sodium salts of sulfated cetyl alcohol, and alkylaryl polyethyl alcohol.

Catalyst charge B comprises a suflicient amount of polymerization catalyst dissolved in water to insure sub- A three-liter glass-lined reaction vessel fitted with a reflux condenser, thermometer and agitator was charged with the reactor charge. After refluxing for l-15 minutes to remove air, the reactor charge was cooled to the stantially complete polymerization, such as a catalyst 5 polymerization temperature of 90-92 C. and maintained mentioned useful in catalyst charge A above. at this temperature during the course of the reaction. The

Monomer charge I consists of a minor portion of the polymerization reaction was then conducted stepwise as vinyl aryl monomer. This is polymerized in the first stage follows: of the latex formation to produce a hard core. Monomer (1) Catalyst charge A was added incrementally at a charge II consists of the unsaturated ester and a major rate of 10 ml./ 10 min. for about 90 minutes. At the portion of the vinyl aryl monomer. This is added subsesame time, monomer charge I was added incrementally at quently to plate the hard core with a soft shell. Therea rate of 10 ml./ 10 min. for the first 60 minutes and then after monomer charge III, consisting of itaconic acid and increased to a rate of 35 ml./ 10 min.

a portion of the catalyst charge A is added to incorporate (2) Monomer charge II was added at a rate of 35 ml./ carboxyl groups into the copolymer. 10 min. until the entire charge was added.

The polymerization is advantageously carried out at a (3) After the first 90 minutes of the polymerization, pH within the acid range, preferably, for example, the monomer charge III was added incrementally at the rate range of 2.5-3.5. After the latex has been prepared, it is of 10 ml./10 min. until the entire amount was added. desirable to raise the pH to from 8-10. Inorganic or Thereafter the remainder of catalyst charge A was added organic bases may be used to adjust the pH of the aqueous incrementally over a period of 90 minutes. At the end solution, such as sodium hydroxide, ammonium hydroxof all of the above additions, catalyst charge B was added ide, potassium hydroxide, monoethanolamine and the like. incrementally at the rate of 5 ml./ 20 min. to completely In the polymerization process the reactor charge is addreact traces of residual monomer. Total reaction time ed to a suitable reaction vessel and heated to a boil to was eight hours. remove oxygen. The temperature is then adjusted to a By this process, a grain-free, coagulum-free latex was conventional polymerization temperature, such as between produced at 90 percent conversion and 50 percent solids. 50 and 100 C., and preferably to a temperature between The pH was adjusted to 9.5 with ammonium hydroxide 85 and 95 C. The polymerization may be conducted and the latex steam distilled to remove the unreacted under subatmospheric, atmospheric or superatmospheric monomers. The final product was a white, non-iridescent pressure, although atmospheric pressure is preferred. latex having a viscosity of 31 cps. and a surface tension The invention is further illustrated by the following exof 37 dynes/ cm. This latex showed good mechanical amples: stability, low foaming, stability to borax, and as a three Example I mil thick dry film on glass, showed tackiness and a minimum film forming temperature of less than 33 F.

A grain-free Was P p according to the 35 Using proportionate quantities. of reactants and the lowing Schedule of charges: same reaction conditions, the process was scaled up Reactor charge: Weight (g) to produce S-gallon and IOU-gallon batches. Similar re- Water 0 s-ults were also obtained by substituting n-butyl acrylate or Catalyst Charge n-butyl methacrylate for 2-ethylhexyl acrylate and by sub Water 29H) stituting alpha-methylstyrene for styrene. Sodium salt of an alkylaryl sulfonate (28% soln.) 82.0 Alkylaryl polyether alcohol 4.5 Example H Sodium pyrophosphate (decahydrate) 2.5 Potassium sulfate 2.4 Using the procedure of Example I, with the excep- Potassium persulfate 3.6 tion that the percent of monomer charges was varied,

TABLE I Itacouic 2-etl1yl- Solids b Percent Mechanical N0. Acid Styrene a hexyl (Theoret- Conver- Stability Acrylatc ical) sion 0.00 55.0 45.0 51.0 98+ Unsatisfactory. 0. 25 55. 0 43. 75 51. 0 98+ Do. 0. 56.0 43. 5 c 48. 0 96 Very Good. 0. 50 55. 0 43. 5 51. 0 98+ Do. 1. 50 55.0 43. 5 51. 0 97 Do. 2. 00 55.0 43. 0 c 48. o d 88 Not Tested. 2.00 55. 0 43. 0 51. 0 d 91 D0.

Weight p erccnt of the total monomers.

b Weight. percent of total latex B Lower theoretical solids resulted in decreased percent conversion.

d Percent conversion was so low that the latex was unsatisfactory and no tes lor1nccl1anical stability was performed.

Catalyst charge B:

Potassium persulfate 0.54

Weight (g) 65 the certain experiments were performed and the results recorded as shown in the table above. It may be concluded from the above table that:

1) The effective range of itaconic acid is between 0.50 and 1.50 percent of the total monomer charged.

(2) The percent conversion is increased at about 51 percent theoretical solids over 48 percent theoretical solids.

Example III.Exteri0r Paint The new latex prepared in Example I was used to make a conventional exterior paint.

Paste recipe: Grams Titanium dioxide 582.5 Calcium carbonate 287.8 Diatomaceous earth 93.2 Alkylaryl polyether alcohol 0.9 Dis'persant 15.3 Ethylene glycol 43.4 Fungicide 2.3 Defoamer 0.5 Water 356.2

This paste was ground and 902.5 g. of latex was added with constant mixing along with a synthetic thickener to thicken the product to 75-78 K.U. viscosity. This prepared about a half gallon having a pigment volume concentration of 42% and total solids content of 56%.

The latex paint was applied as a three mil film to a prime coated glass substrate. After 16 hours at room temperature, scrub resistance was determined with a Gardner Washability Machine. Very little wear was evident after about 15,000 cycles. In comparison, a comparable paint that was com-pounded With a later containing two parts of methacrylic acid failed at 3000 scrub cycles. The new latex paint showed viscosity stability with time, as evidenced 'by very little thickening during storage, even after 500 hours at 50 C. Further, this latex paint has been tested for long range outdoor exposure and has shown excellent weather-ability.

Example I V.Baked Prime Coats 0n Metals The new latex was used to prepare a baked prime coat for metals.

Paste recipe: Grams 6 Vehicle Grams Latex (48% solids) 2285 Chemically modified drying oil and driers 5.25

This paint was cast on zinc phosphated steel panels and baked for 20 minutes at 175 C. Subsequently, these coatings at l to 1 /4 mil thickness were wet sanded, top coated with an acrylic lacquer, and baked at 80 C. for two hours. The total film thickness was at 2.5 to 3.0 mils. These coatings passed the 80 inch-pound impact and the inch flexibility test. In comparison, a cornpa'rable paint that was compounded with a latex that contained two parts of methacrylic acid, failed impact and adhesion tests due to lack of intercoat adhesion.

We claim:

1. A coating composition comprising an aqueous dis persions of a copolymer comprising from 29-49 percent by Weight of an acrylic ester of the formula:

COOR

OI'I2=C wherein R is a saturated alkyl having from 1-20' carbon atoms and R is a member of the group consisting of hydrogen and methyl, from 50 to percent by weight of a vinyl aryl monomer of the formula:

RCH=CH wherein R is a member of the group consisting of phenyl, lower alkyl phenyl, and halophenyl, and from 0.5 to 1.5 percent by weight of itaconic acid.

2. A grain-free, coagulum-free latex composition normally having a particle size of 0.1 to 0.3 micron comprising a copolymer formed by the copoly-merization in an aqueous medium of 2949 parts by weight of 2- ethylhexy'lacrylate, 5070 parts by weight of styrene, and 0.5-1.5 parts by weight of itaconic acid.

References Cited by the Examiner UNITED STATES PATENTS 3,057,812 10/1962 Straughan et al. 26029.6

MURRAY TILLMAN, Primary Examiner.

L. J. BERCOVITZ, Examiner.

E. B. WOODRUFF, Assistant Examiner. 

1. A COATING COMPOSITION COMPRISING AN AQUEOUS DIS PERSIONS OF A COPOLYMER COMPRISING FROM 29-49 PERCENT BY WEIGHT OF AN ACRYLIC ESTER OF THE FORMULA: 